At a highway-rail grade crossing (or simply a “grade crossing”), a rail system crosses a road network at the same level or “grade.” This crossing is somewhat unique in that at this crossing, two distinct transportation modalities, which differ in both the physical characteristics of their traveled ways and their operations, intersect.
The number of grade crossings has grown with the growth in highways. In 2005, there were 248,273 total intersections of vehicular and pedestrian travel-ways with railroads in the United States. This equates to approximately 2.4 crossings per railroad line mile.
In the early days of railroads, safety at grade crossings was not considered to be much of an issue. Trains were few in number and slow, as were highway travelers who were usually on foot, horseback, horse-drawn vehicles, or bicycles. This changed, however, with the advent of the automobile in the early 1900s.
In addition to the possibility of a collision between a train and a highway user, a grade crossing presents the possibility of a collision that does not involve a train. Non-train collisions include rear-end collisions in which a vehicle that has stopped at a crossing is hit from the rear by another vehicle; collisions with fixed objects such as signal equipment or signs; and non-collision accidents in which a driver loses control of the vehicle. These non-train collisions are a particular concern with regard to the transportation of hazardous materials by truck and the transportation of passengers, especially on school buses.
FIG. 1 depicts a conventional highway-rail grade crossing, generally indicated by reference numeral 100, at the intersection of road 102 and railroad tracks 104. Associated with grade crossing 100 is a warning system, which provides train detection and crossing control.
The train detection is provided by track circuit 116 (and grade-crossing predictor controller 106). The track circuit is based upon closed-circuit fail-safe design principles. An interruption or disturbance in the circuitry or in the signals impressed on the rails to detect trains will activate crossing warning devices that are a part of the crossing control system.
The track circuit includes approach circuits 112 and 114 and island circuit 110. Approach circuit 112 is defined between shunt 118A and lead 120A. Approach circuit 114 is defined between shunt 118B and lead 120B. Island circuit 110 is a region of track circuit 116 that is between leads 120A and 120B. The same leads 120A and 120B are used for the island and the approach circuits, although different signals are used.
Crossing control is provided by crossing warning devices 122 (and grade-crossing predictor controller 106). Crossing warning devices 122 provide appropriate warning to vehicles and pedestrians, typically by means of flashing lights 124, movable barrier gates 126, and audible devices, such as bells (not depicted). Warning devices 122 are typically placed on both sides of track 104 and adjacent to roadway 102.
In addition to the aforementioned track circuits (for train detection) and warning devices (for crossing control), the warning system includes grade-crossing predictor controller 106. This controller provides crossing control, train detection, as well as a recording functionality (in some systems) for the grade crossing.
Controller 106 is disposed within weatherproof housing 108, which is usually sited near railroad track 104. Typically, controller 106 includes a display, such as touch screen display that provides a user interface for programming/configuring the controller, such as during initial setup. Controller also typically includes a central processing unit, track modules (e.g., software, etc.) for monitoring track 104, crossing control modules (e.g., software, etc.) for controlling the crossing warning devices 122, and a recorder (not depicted) for recording events and conditions at grade crossing 100. In some prior-art grade-crossing systems, controller 106 is capable of two-way communications via wireless telecommunications devices 128 (e.g., transceiver, antenna, etc.). For example, controller 106 might receive inquiries from and/or transmit information to a railway operations center in conjunction with telecommunications equipment 128.
In addition to any other tasks, controller 106 monitors at least (1) the portion of railroad track 104 that intersects road 102 within island circuit 110 and (2) those portions of railroad track 104 within approach circuits 112 and 114 (to the left and right of the island circuit). When controller 106 detects the presence of a train in approach circuits 112 or 114, or in island circuit 110, the controller activates the flashing lights 124 and the audible devices and causes gates 126 of crossing warning devices 122 to be lowered.
It is required that railroad track circuits actuate active warning devices a minimum of 20 seconds before arrival of a train where trains operate at speeds of 20 mph or higher. Conventional grade-crossing predictor controllers, such as controller 106, are designed to provide a constant crossing warning time for approaching trains. These devices, which are the standard means for train detection in the railroad industry, are tailored for a train approaching at track speed. If, however, a train were to accelerate within approach circuits 112 or 114, the controller will provide a poor estimation of the estimated-time-of-arrival (ETA) and the warning times will not be consistent. The estimate will be even worse when conditions such as a rusty rail or ballast problems are present.
As a consequence, trains that have stopped at a station or trains operating under a restriction near crossings are prevented by operating rules from accelerating at their maximum rate until they have passed nearby highway crossings. Vehicular traffic delays result while the crossings remain actuated until the train passes. This delay is magnified when there are several highway crossings in proximity, as often occurs in urban areas.
As such, from the community viewpoint, there is a concern over delays, congestion, and the impact on emergency vehicle response (due to trains blocking street crossings). Even so, communities often impose speed restrictions on trains, which of course exacerbates delays because trains take longer to clear crossings. From the railroad viewpoint, speed restrictions are undesirable because of the delays incurred by trains as they slow down to pass through a community. As a consequence of these issues, the current practice of existing railroads is to consolidate and close grade crossings where feasible.
It would be advantageous to provide a method for reducing both rail and automotive traffic delays due to the presence of grade crossings.